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A248023
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Even numbers which are neither primes nor perfect powers and are coprime to the sum of their divisors.
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1
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50, 98, 242, 338, 392, 578, 722, 800, 968, 1058, 1250, 1352, 1682, 1922, 2312, 2450, 2738, 2888, 3362, 3698, 3872, 4232, 4418, 4802, 5408, 5618, 6050, 6272, 6728, 6962, 7442, 7688, 8450, 8978, 9248, 10082, 10658, 10952, 11552, 12482, 12800, 13448, 13778, 14450
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OFFSET
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1,1
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LINKS
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EXAMPLE
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50 is in the sequence since it is neither a prime nor a powerful number and its divisors 1, 2, 5, 10, 25, and 50 sum to 93, which is coprime to 50.
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MATHEMATICA
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perfectPowerQ[n_] := n == 1 || GCD @@ FactorInteger[n][[All, 2]] > 1; Select[ 2 Range@ 7500, !PrimeQ[ #] && GCD[#, DivisorSigma[1, #]] == 1 && !perfectPowerQ[ #] &]
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PROG
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(PARI) lista(nn) = {forstep(n=4, nn, 2, if (!ispower(n) && (gcd(n, sigma(n))==1), print1(n, ", ")); ); } \\ Michel Marcus, Oct 02 2014
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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